Counting names within a cell

Hi,

I have many rows of data formatted in the following way within each cell.

43598: Joe Bloggs
38768: John Smith
97568:
87231: John Smith


I would like to count the number of times in each cell that a reference number appears but no name is present next to it (i.e. 1 in the above example). The result can appear in a seperate column next to the data.

I would assume this is something that could be done with counting the length between carriage returns and/or related to the colons after the reference numbers, unfortunately my excel skills have not come up with a solution and I have not found anything similar enough by searching.

If this is possible, I am not bothered whether I end up using a cell formula or VB code.

thanks in advance.